Pneumatically operated mixing device

ABSTRACT

A pneumatically-driven mixing device includes a &#39;&#39;&#39;&#39;Beams top&#39;&#39;&#39;&#39; to rotate a relatively stiff shaft to the end of which may be affixed a mixing paddle or the like. The &#39;&#39;&#39;&#39;Beams top&#39;&#39;&#39;&#39; provides a simple mixer drive capable of substantial rotational velocities, but which will suffer no significant damage if the shaft is jammed or stalled.

United States Patent Bannister [451 July 10,1973

[ PNEUMATICALLY OPERATED MIXING DEVICE [75] Inventor: John D. Bannister, Dover, Mass.

[73] Assignee: Damon C0rporation,Needham Heights, Mass.

22 Filed: Oct. 22, 1911 21 Appl. No.: 191,883

[52] US. Cl 259/108, 415/503, 308/D1G. ll [51] Int. Cl B0lf 7/16, 1301f 15/00, F16C 32/00 [58] Field of Search 259/7, 8, 23, 24, 259/43, 44, 107, 108; 415/503; 416/176;

308/D1G. ll

[56] References Cited UNITED STATES PATENTS l/1968 Ferrante 259/107 X 3,210,848 lO/l965 Bizzigotti 415/503 X 3,014,437 12/1961 Dutchess 259/108 FOREIGN PATENTS OR APPLICATIONS 734,330 7/1955 Great Britain 259/8 999,699 10/1951 France 415/503 OTHER PUBLICATIONS Beams, .1. W. An Apparatus for Obtaining High Speeds p of Rotation. In Rev. of Scientific Instruments Vol. I,

1930, p. 667-671. Q184.R5.

Garman, w. o. A Study of the High-Speed Centrifuge In Rev. of Scientific Instruments Vol. 4, 1933, p. 450-453. 0184.115.

Beams, .1. W. and Pickels, E. G. The Production of High Rotational Speeds. In Rev. of Scientific Instruments, Vol. 6, 1935 p. 299-308. Q184.R5.

Beams, J. W., Linke, F. W., and Sommer, P. A Vacuum Type Air-Driven Centrifuge for Biophysical Research In Rev. of Scientific Instruments Vol. 9, 1938, p.

Beams, J. W. High Rotational Speeds in Journal of Applied Physics Vol. 8, 1937, p. 795-806. QCI.J82.

Primary ExaminerWayne A. Morse, Jr. Assistant ExaminerPhilip R. Coe Attorney-Clarence S. Lyon 5 7 ABSTRACT 9 Claims, 3 Drawing Figures United States Patent m: [H] 3,744,766

7 Bannister July 10, 1973 1 PNEUMATICALLY OPERATED MIXING DEVICE FIELD OF THE INVENTION The invention relates to a pneumatically-driven mixing device particularly adapted for use in automated chemical processing equipment.

BACKGROUND OF THE INVENTION In recent years automatic equipment for carrying out chemical analyses has come into extensive use. In such equipment typically a sample to be analyzed may be deposited in a container carried by a conveyer. A reagent or set of reagents specific to a particular substance in the sample is added to the container and the reaction which leads to a change in some physical property of the sample e.g. color then proceeds as the container is carried along by the conveyer. After a time, the reacted reagent and sample are removed, and the physical property measured to-determine the amount of the particular substance in the sample for which the reagent or set of reagents was specific. A machine of this general character particularly useful for analysis of blood serum is shown in the copending application of Kosowsky et al, entitled Constituents Measuring Chemical Analyzer Having Multiple Concurrently Operated Aliquot Processing Conveyers, Ser. No. 105,805 filed Jan. 12, 1971 which is assigned to the assignee of the present application.

It is of course highly desirable to mix the sample and reagent or set of reagents during the reaction process. While some reactions may proceed with sufficient vigor, or the sample and reagent may be sufficiently miscible that adequate results are obtained with only limited mixing, some proceedures may require vigorous mixing.

Heretofore mixers of various types have been used for this purpose. One type includes a high speed electric motor supported above the container and having a shaft which extends downwardly into the container. The shaft may or may not have a paddle or other device on it to enhance mixing. Such electric motors perform mixing satisfactorily. However, if the shaft becomes jammed as a result of conveyer indexing for example the motor may be damaged if it remains connected to a power source. Additionally electric motors require that electric power be provided in an environment which may at times include highly conductive liquids. This means that the motor wiring must be protected from damage as a result of liquid impregnation, all at substantial expense.

In general machines of the type described have available a supply of compressed air which can be used to drive an air turbine at substantial velocity. However air turbines generally operate at very high speeds and, for analysis of blood serum, may denature the proteins in the serum. Further, most air turbines have a rotor supported by at least two bearings. Thus the shaft of such a mixer is located in a fixed position and in a malfunctioning automatic machine may be jammed or bent.

GENERAL DESCRIPTION OF THE INVENTION To overcome the foregoing problems, I have provided a mixer which utilizes a Beams top to provide the driving force. As used herein the term Beams Top" will be used to describe an air-driven turbine which has a conically-shaped rotor supported on an air film within an approximately similarly shaped conical Beams top include the following: Author Title J.W. Beams Publication An apparatus For Obraining High Speeds of Rotation"l Rev. of Scientific Instruments PP 667 et seq. (hereinafter R.S.I.) November,

1930 W.D. Garman A Study of the High-Speed Centrifuge"4 R.S.I. PP 450 et seq.

August, 1933 .I.W. Beams and The Production of High Rotational Speeds4 R.S.l. pp 299 et seq.

October, 1935 E.G. Pickels .LW. Beams High Rotational Speeds8 Journal of Applied Physics PP 795 et seq. October, 1937 .I W. Beams A Vacuum Type Air-Driven Centrifuge for Bio-physical Research9 R.S.I. PP 248 et seq.

August. 1938 F.W. Lenke P. Sommer It is apparent from the titles of the foregoing publications as well as the content of the articles that the Beams top was considered to be a device whose principal property was its high rotational speed. It was used as a centrifuge or to carry on the rotor a device which it was desired to rotate at high speed e.g. a mirror. One use described in the foregoing publications was to drive an ultracentrifuge rotor through a flexible shaft described as a piano wire.

Because of its extremely high speed and relatively low torque it would not normally be considered useful as a drive for a mixing device. However, I have found that mixers using a Beams top with a relatively heavy stiff shaft extending downwardly from the rotor into the material to be mixed will mix with great efficiency. Their speed may be controlled quite readily by controlling the supply air pressure and flow. They are particularly advantageous in automatic machines in that no conventional bearings are required. Thus the shaft is essentially free of any fixed position with respect to the stator and thus is less likely to be jammed or bent by machine malfunction. Further, if the shaft is stalled, there is no burn-out, since the air supply merely passes harmlessly away from the turbine. Finally the mixers of my invention are simple and economical in construction. In an automatic machine which may require a significant number of such mixers this latter fact is an important consideration.

DESCRIPTION OF THE DRAWING A more complete description of mixing devices made according to my invention is included in the following detailed description and in the accompanying drawing in which:

DESCRIPTION OF ILLUSTRATED EMBODIMENT As shown in the drawing, the mixing device includes a stator member, generally indicated at and shown in FIGS. 1A and 18, a rotor member, generally indicated at 32 and shown in FIG. 2. A shaft 38 depends from the rotor and is formed as a mixing paddle at its lower end.

The stator member 10 is substantially cylindrical in shape with a flange l2 integrally formed with the body of the member at the upper portion thereof. A bore 14 extends through the center of the stator member 10 to receive the shaft attached to the rotor. A depression 16 having the shape of a truncated cone is formed in the upper surface of the stator to receive the cone-shaped portion of the rotor to be hereinafter described. Typically the included angle of the cone-shaped depression in the stator is of the order of 91 to 93.

A circular member 18, L-shaped in cross section is secured to the underside of the flange 12 and the side wall of the stator. This member may be secured in any convenient fashion as by welding, brazing or the like. The annular space 20 defined by the stator and the inner surface 18a of the member 18 constitutes a manifold to supply air or other gas under pressure to a plurality of passages 22 which extend from the manifold 20 to the surface of the cone-shaped depression 16. In the drawing six of these passages 22 have been shown, but this number may vary from as low as one to as high as twenty or thirty.

As shown in FIG. 1B, the axis of the passages makes a horizontal angle H with the radius of the stator member. Also as shown in FIG. 1A, the axis of the passages 22 make an angle V in the vertical plane with respect to the horizontal. I have found that extremely stable operation is obtained if the angle H is 65 and the angle V is 35.

Pressurized air or other gas is supplied to the manifold 20 via the inlet tube 24, to the inlet end of which may be secured a flexible air hose 26. A bushing 28 is desirably located at the bottom of the bore 14 to prevent whipping of the relatively long mixer shaft.

Typically, the stator may be supported through a hole formed in a mounting plate 30. As will be explained below the rotor, shaft and mixing blade are supported above the stator on a thin film of air.

The rotor, shaft and mixing paddle are illustrated in FIG. 2. The rotor, generally indicated at 32, includes an upper substantially cylindrical portion 34 and a lower cone-shaped portion 36. A shaft 38 is secured in any convenient manner to the rotor 32 and extends downwardly from it. The shaft may be flattened to form a paddle 40 and the paddle-shaped portion may be twisted through 90 as at 40a to further enhance mixing. It is highly desirable, to insure proper mixing that the end of the mixing shaft extend close to the bottom of the mixing vessel. Thus, in FIG. 2, the paddle portion of the shaft 40 is shown immersed within the hemispherical bottom portion of a conventional test tube 42.

The shaft 38 may be hollow or it may be solid. I have found that a hollow shaft is preferable to a solid one because it results in a lower weight and therefore an easier starting.

Flutes or buckets, generally indicated at 44 are formed in the surface of the cone-shaped portion 36 of the rotor 32. While various shapes of such buckets may be used, the buckets on mixing units which have actually been made were formed with an end mill whose longitudinal axis was positioned so that it made a horizontal angle of about 65 with the rotor radius. The longitudinal axis of the end mill was substantially perpendicular to the vertical axis of the rotor while the buckets were being formed. The actual buckets were made by touching the surface of the rotor with an end mill.

The rotor 32 may be advantageously formed of plastic or metal material. In general metals are denser than plastic materials and therefore tend to provide lower speeds of rotation and greater stability than plastic materials.

A mixer made according to my invention had the following dimensions. The stator diameter was threeeighths inch, the diameter of the flange 12 was about one-half inch, the overall height of stator 10 was threefourths inch and the height of the portion above the plate 30 was five-sixteenths inch. The holes 22 were drilled with a one thirty-second inch twist drill. The diameter of the portion 34 was three-eighths inch and about three thirty-seconds inch high. The height of the conical portion was about five thirty-seconds inch and the overall height of the rotor about one-fourth inch. The shaft diameter was about one-sixteenth inch and the shaft was about 4 inches in length. The included angle of the conical portion was about lOl-l03.

The buckets or flutes were formed in the upper half of the conical surface and there were about 13 of them.

In operation the rotor 32 is placed so its conical surface opposes the conical surface 16 in the stator with the shaft 38 passing downwardly through the bore 14. Airis supplied under pressure to the manifold 20 and is guided by the passages 22 so that it impinges on the buckets 44 to cause the rotor to rotate. The air also lifts the rotor so that the rotor cone is no longer in engagement with the conical surface 16 of the stator. Rather there is a thin film of air at low pressure between the two. Air passing up the bore 14 to this low pressure area aids in stabilizing the device. The bushing 28 is not a bearing and in some instances may be unnecessary. It does aid in preventing the relatively long shaft 38 from whipping.

The speed of the mixer may readily be controlled by adjustment of the supply air pressure. Air pressures of 2 to 5 p.s.i. 6 create speeds of a few hundred r.p.m. which are adequate for mixing most aqueous solutions. Viscous solutions may require pressures to 10 p.s.i. 6

While I have found that satisfactorily low rotational speeds may be obtained by use of a solid shaft, in some instances a dynamic braking effect may be obtained by locating vanes or blades on the top surface of rotor 34 to further reduce the speed of the rotor.

It will be observed that there is no physical connection between the rotor and shaft and the stator (except for possible frictional engagement at the bushing 28). Thus the shaft may be jammed or pushed upwardly and to a significant extent sideways without any damage to the mixer. The mixer is a relatively low torque device and slows down substantially when placed in liquids to be mixed. When it is removed from the liquid it speeds up appreciably, flinging off droplets of the liquid that may have adhered to it, thus cleansing the mixing paddle and shaft. Under some circumstances, in automatic machines, it may be desirable to program the supply pressure so that it is increased when the mixer shaft is removed from the liquid, to thereby increase the rotational speed and enhance this cleaning action. Mixing may also be enhanced by varying pressure and hence speed while mixing.

It will thus be seen that I have provided an improved mixing device using an air driven Beams top as a driving unit and having depending from the rotor thereof a relatively rigid shaft to engage the material to be mixed. As previously discussed the mixer of my invention is particularly useful in automatic chemical analysis machines, although not limited to such use. It is simple and economical in construction and yet will withstand substantial machine malfunction without damage.

Having described my invention, 1 claim:

1. A pneumatically driven mixing device comprising, in combination:

a. a stator member, said member having a bore free of friction reducing mechanical bearings therethrough and a conical depression formed in its upper surface;

b. a manifold;

c. means supplying gas under pressure to said manifold;

d. at least one passage in said stator leading from said manifold to the surface of said conical depression to supply gas to said surface, the axis of said passage being inclined toward said surface and making a substantial angle with respect to a radius of said stator in a first plane perpendicular to the axis of said bore;

e. a rotor having a cone-shaped lower surface, and

having a plurality of buckets formed in said coneshaped surface, said rotor and stator forming a Beams top;

f. a relatively stifi shaft depending from said rotor through the bore in said stator to engage the material to be mixed.

2. The combination defined in claim 1 in which a mixing paddle is affixed to the lower end of said shaft.

3. Thecombination defined in claim 2 in which said mixing paddle includes at least a twist.

4. The combination defined in claim 1 in which the angle of inclination of said passage is about 35 measured from the base of said passage in a plane, containing the axis of said passage, and being perpendicular to said first plane.

5. The combination defined in claim 1 in which the angle of inclination of said passage to said stator radius in said first plane is about 65.

6. The combination defined in claim 1 in which the angle, included between two rays formed by the intersection of said conical stator surface and a plane containing the axis of symmetry of said conical depression, is between 91 and 93.

7. The combination defined in claim 6 in which the angle, included between two rays formed by the intersection of said conical rotor surface and a plane containing the axis of symmetry of said conical rotor surface, is between 101 and 103.

8. A pneumatically driven mixing device comprising, in combination,

a. a Beams top having a rotor and stator;

b. a relatively stiff shaft depending from the rotor of said Beams top through a bore, free of friction reducing mechanical bearings, in the stator thereof to engage the material to be mixed below said top; and

c. means for supplying air under pressure to cause rotation of said rotor and the shaft attached thereto.

9. The combination defined in claim 8 in which said shaft includes a mixing paddle affixed to the end thereof.

Patent No. 3,744, 766 Dated July 10, 1973 Inventor-(S) John D. Bannister It is certified Lhat error appears in the above-identified patent A and that said Letters Patent are hereby corrected as shown below:

Column 2, lines ll through 28 reading Author Title Publication J.W. Beams 4 T 'An apparatus For Obraining High Speeds of Rotation"lRev. of Scientific Instruments PP 667 et seq. (hereinafter R.S.I.) November, 1930 W.D. Garman I "A Study of the High-Speed Centrifuge"4 R.S.I. PP 450 et seq.

. August, 1933 J.w. Beams and "The Production of R.S.I. pp 299 et seq.

' High Rotational Speeds4 October, 1935 E.G. Pickels J'.W.Beams High Rotational Speeds8 Journal of Applied 4 Physics PP 795 et seq.v October, 1937 J.W. Beams A Vacuum Type Air-Driven Centrifuge for Bio-physical Research9 R.S.I. PP 248 et seq.

August, 1938 F.w. Lenke P. Sommer um'ngu S'lAIES PATENT OFFlCE (fl l'l'li'l 1 Fl CA TE 0 1* CO RR E CT l ON Patent 11... 3,744,766 Dated July 10, 1973 lnvenwfls) John D. Bannister I Page 2 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

should read Author Title 7 Publication J.W. Beams "An Apparatus For Obtaining 1 Rev. of Scientific High Speeds 0f Rotation" Instruments PP 667 et seq. (hereinafter "R. S. 1.") Nov. 1930 W.D, Garman i "A Study of the High-Speed 4 R. S.'I. PP 450 et Centrifuge" seq. August, 1933 J.W.'Beams and "The Production of High 6 R.S.I. PP 299 et E.G. Pickels Rotational Speeds" seq. October, 1935 J.W. Beams "High Rotational Speeds" 8 Journal of Applied Physics PP 795 et seq October, 1937 J.W. Beams "A Vacuum Type Air-Driven 9 R. S. I. PP 248 et F.W. Lenke Centrifuge for Bioseq. August, 1938 P. Sommer physical Research" Column 4, line 46 reading 2 to 5 p.s.i. 6 create speeds of a few hundred r.'p.m.

1 should read 2 to '5 p.s.i.g. create speeds of a few hundred r.p.-m-.

Signed and sealed this 13th day of August 1971+.

(SEAL) Attest:

MCCOY GIBSON, JR. 0. MARSHALL DANN Attestlng Officer Commissioner of Patents I A I; FORM Po Ho I USCOMM-OC 603764 09 1 u s covumuun umvmr. OHICI: Ill o-su-Lu 

1. A pneumatically driven mixing device comprising, in combination: a. a stator member, said member having a bore free of friction reducing mechanical bearings therethrough and a conical depression formed in its upper surface; b. a manifold; c. means supplying gas under pressure to said manifold; d. at least one passage in said stator leading from said manifold to the surface of said conical depression to supply gas to said surface, the axis of said passage being inclined toward said surface and making a substantial angle with respect to a radius of said stator in a first plane perpendicular to the axis of said bore; e. a rotor having a cone-shaped lower surface, and having a plurality of buckets formed in said cone-shaped surface, said rotor and stator forming a Beams top; f. a relatively stiff shaft depending from said rotor through the bore in said stator to engage the material to be mixed.
 2. The combination defined in claim 1 in which a mixing paddle is affixed to the lower end of said shaft.
 3. The combination defined in claim 2 in which said mixing paddle includes at least a 90* twist.
 4. The combination defined in claim 1 in which the angle of inclination of said passage is about 35*, measured from the base of said passage in a plane, containing the axis of said passage, and being perpendicular to said first plane.
 5. The combination defined in claim 1 in which the angle of inclination of said passage to said stator radius in said first plane is about 65*.
 6. The combination defined in claim 1 in which the angle, included between two rays formed by the intersection of said conical stator surface and a plane containing the axis of symmetry of said conical depression, is between 91* and 93*.
 7. The combination defined in claim 6 in which the angle, included between two rays formed by the intersection of said conical rotor surface and a plane containing the axis of symmetry of said conical rotor surface, is between 101* and 103*.
 8. A pneumatically driven mixing device comprising, in combination, a. a Beams top having a rotor and stator; b. a relatively stiff shaft depending from the rotor of said Beams top through a bore, free of friction reducing mechanical bearings, in the stator thereof to engage the material to be mixed below said top; and c. means for supplying air under pressure to cause rotation of said rotor and the shaft attached thereto.
 9. The combination defined in claim 8 in which said shaft includes a mixing paddle affixed to the end thereof. 